The three-dimensional center of gravity (hereinafter referred to as “CG”) of an object can be calculated using a single static platform. However, in this case, the object must still rotate relative to the plane normal to the gravity vector. This method calculates two separate two-dimensional centers of gravity while the object is balanced on two unique planes. Two unique lines are created beginning from each 2D center of gravity and extending in the directions normal to the respective planes on which the object sits. The intersection of these two lines gives the three dimensional center of gravity. One major disadvantage of this method is that many objects do not have two unique planes that can hold the object at equilibrium. This introduces many measuring inaccuracies and will also create imprecise results. Another disadvantage is that two disparate sets of constraint equipment will be required to hold the object in the two positions.
Another prior method of measuring CG is the “hang from a string” method. The hang from a string method also requires two unique lines through an object to calculate the 3D CG. If an object is hung by a single string, the CG of the object will fall inline with the string supporting the object. Once the object has been hung from two separate locations on its body, the two unique lines will intersect at the three dimensional CG of the object. This method is inaccurate for many reasons. There is no straightforward way to measure the direction of the unique lines as they pass through the object, hence the intersection of the two lines will have great inaccuracies. Additionally, this method is not practical for objects weighing more than ten or fifteen pounds as it becomes very hard to lift and manipulate them correctly using a thin cable.
Based on volume and density characteristics, many Computer Aided Design (“CAD”) programs can accurately and precisely calculate the center of gravity of a single object or of an assembly of objects. This method is recommended for very well defined systems, where parts are accurately modeled, material properties are well defined, and all of the system's components are included in the CAD model. However, many real world objects are made of literally thousands of components that have unknown geometries and or material properties. In many cases, it is not feasible (or even impossible) to manually define the shapes and densities as required to create an accurate CG location. A final disadvantage of this system is that it cannot account for parts with variable densities.